Emacs builds on macOS 10.13.6 do not show scroll bars even if both vertical and horizontal ones are enabled. The attached screenshot refers to 'Emacs -Q'. 

It seems that the "places" where scroll bars should appear are drawn but not the scroll bars. Clicking there looks as if the scroll bars are hidden.

Rebuilding an old master,

1)
commit: d2d3fc39295953b4db5bdd7a21d513a87d3d00f0
Alan Third 2021-07-26 23:12:31 +0100
Convert fringe bitmaps to vectors on NS port

produce an Emacs which DOES HAVE scroll bars!

The first build in which scroll bars are gone or hidden looks

2)
commit: a4d2c88cdee90a3e4863a62c4ff69896d0c1a347
Alan Third 2021-07-31 11:13:05 +0100
Simplify macOS drawing code

So, something changed between 2021-07-26 and 2021-07-31 seems to have broken this features.

I already flagged this on emacs-devel (https://lists.gnu.org/archive/html/emacs-devel/2021-12/msg03194.html) and re-flagged here to have memory of this issue.

Ciao,
  Angelo.